The present invention relates to I/O modules for industrial control systems and in particular to a low heat dissipation I/O module that may flexibly accommodate input AC waveforms over a range of AC voltages.
Industrial controllers are specialized computer systems used for the control of industrial processes or machinery, for example, in a factory environment. Industrial controllers differ from conventional computers in a number of ways. Physically, they are constructed to be substantially more robust against shock and damage and to better resist external contaminants and extreme environmental conditions. The processors and operating systems are optimized for real-time control and execute languages allowing ready customization of programs to comport with a variety of different controller applications. Typically, the controllers have a highly modular architecture that allows different numbers and types of input and output modules to be used to connect the controllers to the process or machinery to be controlled. This modularity is facilitated through the use of special “control networks” suitable for highly reliable and available real-time communication. Such control networks (for example, Ethernet IP) differ from standard communication networks (e.g. Ethernet) by guaranteeing maximum communication delays, for example, as obtained by pre-scheduling the bandwidth of the network, and/or providing redundant communication capabilities to high-availability.
As part of their enhanced modularity, industrial controllers may employ I/O modules dedicated to a particular type electrical signal and function, for example, detecting input AC or DC signals or controlling output AC or DC signals. Each of these I/O modules may have a connector system allowing them to be installed in different combinations in a housing or unit along with other selected I/O modules to match the demands of the particular application. Multiple units may be located at convenient control points near the controlled process or machine to communicate with a central industrial controller via a special control network such as Ethernet IP. Normally different I/O modules are required for receiving different AC and DC signals from the industrial processes or machinery, reflecting differences in the devices used. Different I/O modules may be used, for example, for receiving input signals operating around 120 volts AC as opposed to 240 volts AC.
The circuitry of the I/O module communicating with the industrial controller (controller-side) is also typically optically isolated from the circuitry communicating with the controlled process or machine (field-side) in order to prevent faults in the field-side from damaging the industrial control system or other I/O modules. For input circuits (such as AC input circuits) it can be necessary to receive the voltage signal from operation of the field-side circuitry to determine the frequency and/or amplitude of the signal from the controller-side. To prevent excess power from damaging the I/O module, a voltage dropping series resistor is often used converting the high voltage from the field-side into a lower voltage suitable for optical isolation to the controller-side. Such voltage dropping series resistors are often physically large to handle the necessary power dissipation and must be spaced apart to aid in dissipating the incident heat.